Boiler screws

[Speedy Builder5Participant @speedybuilder5]

Material for boiler screws

[Speedy Builder5Participant @speedybuilder5]

Getting on well with a copper boiler for 5" Speedy but seek recommendation for the best material to use for bolts used for fittings. These bolts go into bronze bushes. In testing, I have used steel bolts (7 & 8 Ba), but some of these have rusted, and to date, one has sheared off. Is stainless a viable alternative and if so, which grade.

Bob H

[GoCreateParticipant @gocreate]

Hi Bob

431S29T or En57T is a high strength st st and offered by some ME suppliers. I used this on boiler fittings for my 3" Allchin TE.

However, your joints are limited by the thread stripping strength in your bronze bush so using a high strength st st may be OTT, in which case I would suggest 316 st st would be OK as well.

Avoid 303 st st which is not generaly suitable for higher stressed or critical components.

Hope this helps.

Nigel

 

Edited By tractionengine42 on 22/10/2013 21:12:00

[Speedy Builder5Participant @speedybuilder5]

Thanks for the comprehensive reply Nigel. It seems to me that the strength is more important for getting the bolts out more than holding the fitting in place. So I guess the question now is – Any suggestions for suppliers of the above Stainless bolts 7 & 8 Ba in small quantities.

Bob H

[DustyParticipant @dusty]

Hi Speedy

Bolts should not be used for boiler fittings, you should use studs and nuts. Having said that you will have great difficulty in finding any 7 or 8ba stainless bolts or even studs. 7ba is not much of a problem as you can make them from 2.5mm stainless bar. 8ba is problematic in that you need 2.2mm dia and as far as I can see is as rare as rocking horse turds. I am not aware of any supplier who does either 7 or 8ba stainless bolts. I am sure that of all those who range under our banner someone will know of a supplier. The other option is stainless steel studding not ideal but is an option.

[Bob YouldonParticipant @bobyouldon45599]

Hi Speedy,

As Dusty has already mentioned, studs should be used for attaching boiler fittings to boiler facings, these should be proper studs and not pieces of threaded rod but proper plain waisted studs; ideally the material should be a good quality stainless or drawn bronze, monel is a first class material for the type of use you envisage. Each stud should be fitted with a spot of graphite grease and ideally each nut would be best made from bronze and fitted with a washer under the nut, again anoint all the threads with a spot of graphite grease before fitting. Bolts and in particular mild steel bolts should be avoided at all costs.

Incidentally monel makes for an ideal material for valve spindles and the like.

Regards,

Bob Youldon

[Speedy Builder5Participant @speedybuilder5]

Thanks for your suggestions.

8Ba studs – I don't think I have the skill and the right sort of lathe (Boxford 4 1/2inch) to make proper studs that small. What, apart from being true scale would be the strength difference between studding and proper waisted studs ?

Thanks for your suggestions

BobH

[Sub MandrelParticipant @submandrel]

EKP supplies do bronze fixings.

Neil

[julian atkinsParticipant @julianatkins58923]

i turn up all my own bolts and studs in stainless and use non magnetic stainless for boiler work. i dont see why a 4.5" boxford cant turn up small stuff unless it's completely knackered! i have on a occasions turned up many 10 BA and 12 BA bolts and studs. never ever use ordinary steel or magnetic steel on boilers, and i wouldnt use bronze compared to stainless due to the lack of shear strength.

cheers,

julian

Edited By julian atkins on 24/10/2013 02:08:55

[Bob YouldonParticipant @bobyouldon45599]

Good morning Speedy,

The difference between using proper plain waisted studs and studding in their shear and yield strength would not be very different, if at all, the strength being dependent upon the core cross sectional area of the thread, the plain section is generally left at full diameter as it is probably more at risk of corrosion whereas the thread in the boiler facing is protected somewhat by the surrounding material and by the nut. Little studs of the correct pattern will take a little longer to make but generally there are no more than a couple of dozen required for a miniature locomotive and furthermore they can be formed from the correct materials.

With care the manufacture of purpose made studs should be possible with your Boxford using ordinary HSS cutting tools which I find to be far more effective than tipped tooling.

Regards,

Bob. . . . .

[Speedy Builder5Participant @speedybuilder5]

Sounds like it is 'Off to the workshop' to see if I can do a Proper Job.

Thanks

Bob H

[Gill Lewis 1Participant @gilllewis1]

Freelance Loco Cylinder C/L.

I wonder if someone could advise me please, on side-play for con rods and coupling rods on the driving crank pin.

If, for example, the play is .020 overall, should the rods have this amount split between them, giving .005 on the four sides of the rods.

I am trying to ensure the cylinder bore c/l is correct to the con rod c/l with wheels equally spaced to frames.

Any help would be much appreciated.

[SpringbokParticipant @springbok]

Strangly I was haveing a chat with one our boiler inspectors and he reccomended bronze bolts
Bob

Edited By Springbok on 04/12/2013 14:45:18

[michael howarth 1Participant @michaelhowarth1]

Picking up the wrong die when about to cut a 7BA thread, I found quite accidentally that 3/32" stainless (0.007" oversize) will produce a very nice 8BA thread if run up with an 8BA die which has been very slightly opened and then finished off with a second run with the die in the normal position.

Mick

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